1. Field of the Invention
The present invention relates to a reciprocating compressor, and more particularly to a reciprocating compressor for increasing volumetric efficiency and compression efficiency of a compressor and for reducing fatigue phenomenon of the compressor by decreasing re-expansion of high pressure refrigerant by exhausting high pressure refrigerant gas existing in an allowance space of a cylinder. High pressure refrigerant is also exhausted when liquid refrigerant exists in the cylinder to prevent over pressure at an initial operation of the compressor.
2. Description of the Prior Art
Generally speaking, a reciprocating compressor, as illustrated in FIG. 1, has a construction disposed with a driving unit 1 and a compression unit 2 within an airtight vessel 100, where the driving unit 1 comprises a motor.
The motor comprises a rotor 120 and a stator 130, where the rotor has a rotating shaft 110.
The compressing unit 2 comprises: an eccentric shaft 212 coupled eccentrically to a lower end of the rotating shaft 110, a connecting rod 214 rotatively coupled to the eccentric shaft 212; a piston 210 rotatively coupled to the connecting rod 214; a circular cylindrical cylinder 200 containing the reciprocating piston 210; and a valve plate 230 and a head cover 220 coupled to one side of the cylinder 200.
The reciprocating compressor thus constructed is commonly installed on a refrigerator, air conditioner and the like to suck in circulating refrigerant gas, and discharge the gas in a high pressure and high temperature state.
When the motor comprising the rotor 120 and the stator 130 is input with electric power, the rotor 120 is rotated to rotate the rotating shaft 110.
When the rotating shaft 110 is rotated, the eccentric shaft 212 is rotated, and when the eccentric shaft 212 is rotated, the crank shaft 214 reciprocates.
When the crank shaft 214 reciprocates, the piston 210 reciprocates linearly within the cylinder 200.
When the piston 200 reciprocates within the cylinder 200, the refrigerant gas circulating in the vessel 100 is sucked into the cylinder 200 to thereby be compressed to a high pressure and high temperature state, and be discharged to the outside of the cylinder 200.
FIG. 2 is a sectional drawing for illustrating an enlarged construction of the compression unit 2 in the reciprocating compressor thus described.
The compressing unit 2 comprises: the eccentric shaft 212 coupled eccentrically to the lower end of the rotating shaft 110; the connecting rod 214 rotatively coupled to the eccentric shaft 212; the piston 210 rotatively coupled to the connecting rod 214; the cylindrical cylinder 200 for reciprocating the piston 210; the valve plate 230 coupled to one side of the cylinder 200; and the head cover 220.
Meanwhile, the cylinder has a circular cylindrical shape open on both sides, and the piston 210 can be inserted into one side of the cylinder 200 and the valve plate 230 and head cover 220 are coupled to the other side of the cylinder 200.
The head cover 220 is partitioned into a suction chamber 221 and a discharge chamber 222 by a bulkhead 223, and the valve plate 230 is disposed with a suction port 231 penetrating the cylinder 200 and the suction chamber 221, and a discharge port 232 and the cylinder 200 penetrating the discharge chamber 222.
The suction port 231 and the discharge port 232 are disposed with a suction valve 232 and a discharge valve 234 respectively.
In the conventional compressor thus constructed, as illustrated in FIG. 2a, the eccentric shaft 212 of the compressor 2 rotates to retract the piston 210 according as the rotating shaft of the motor rotates.
According as the suction value 233 is opened and the discharge valve 234 is closed, the refrigerant gas (in low temperature and low pressure state) in the suction chamber 221 is flowed into the cylinder 200.
Meanwhile, as illustrated in FIG. 2b, when the piston 210 is advanced, the suction valve 233 is closed, and when the discharge valve 234 is opened, the refrigerant gas in the cylinder 200 is compressed to the high pressure and high temperature state, and the compressed refrigerant gas is discharged to the discharge chamber 222 through the discharge port 232.
Even though the refrigerant gas is compressed by the maximum advancement of the piston into the cylinder 200 in the above-indentified process, there still remains an allowance space for the compressed refrigerant gas in the cylinder 200 between the piston 210 and the valve plate 230, which is called an allowance volume V.
The allowance volume V is generated to give an allowance niche between a front of the piston 210 and the valve plate 230 in order to prevent the front of the piston 210 from colliding with the valve plate 23 of the cylinder 200 or to prevent the over-compression from occurring.
Furthermore, the allowance volume V can also be determined by the volume or the like occupied by the discharge port 232 disposed on the valve plate 230.
However, because the suction and discharge processes of the refrigerant gas occur in an instant, and the refrigerant gas remaining in the allowance volume V is re-expanded in a partial discharge state during the suction process right after the discharge of the refrigerant gas, the effective volume within the cylinder 200 is reduced that much to thereby decrease the refrigerant gas volume which is sucked in.
In the aforesaid description, volume loss resulting from the reexpansion of the refrigerant gas which has remained in the allowance volume V is represented by region between points "V1'- V1" in FIG. 6.
In FIG. 6, the region between points "V2 - V1" denotes theoretical effective volume in case of no reexpansion, while "V2 - V1" denotes an effective volume in case of the reexpansion for an actual cycle.
Accordingly, the suction volume of the refrigerant gas is reduced to relatively decrease the discharged volume thereupon, so that compression efficiency of the compressor goes down.
Furthermore, if residual refrigerant in a liquid state remains in the cylinder 200 at the initial operation of the compressor, the over pressure is generated. In the absence of preventive measures, there arises a problem in that the fatigue phenomenon resulting from the over pressure gets worse.
For example in Japanese laid open utility model Publication No. 2-76181 entitled, "Reciprocating Compressor, a technique is disclosed wherein an orifice always interconnecting an interior of a cylinder and a low pressure side of an exterior of the cylinder in a reciprocating compressor, the compressor being similar to that described above, wherein gas is sucked into the cylinder by the reciprocating motion of a piston disposed within the cylinder, and simultaneously the gas is compressed to thereby be discharged.
According to the Japanese laid open utility model Publication No. 2-76181 the reexpansion of refrigerant compressed at high pressure, or the generation of over pressure of the refrigerant at the initial operational stage caused by residual liquid refrigerant can be prevented.
However, the Japanese laid open utility model application No. Hei 2 - 76181 involves a problem in that the compression efficiency can be markedly decreased because an interior of the cylinder and an exterior of the cylinder are always open therebetween.
Furthermore, in a Japanese laid open utility model application No. Hei 2 (1990) - 3082 entitled "piston device of compressor," there is described a compressor comprising a cylinder; a piston reciprocating within the cylinder; and a piston ring contacting an inner wall of the cylinder fitted into a ring groove disposed on an outer side of the piston. Also described therein is a technique where a piercing port for communicating with the ring groove and a cylinder inner socket is disposed at a rear end side of the piston ring, and a hole is formed within the ring groove on a side thereof where the piston ring is contacted.
According to the Japanese laid open utility model application No. Hei 2 - 3082, it seems that the refrigerant gas infused into the ring groove is discharged toward a low pressure side through the hole during a compression stroke to thereby prevent to a degree over compression caused by the liquid refrigerant infused into the cylinder during the initial operation. However, there remains a problem in that a decrease of compression efficiency cannot be avoided that is caused by the reexpansion of the compressed refrigerant gas still remaining in the allowance space.